TREMATODES
Faculty: AGUAZIM SAMUEL, M.D.
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A 34-year-old Brazilian man presented with a 24-year history of prominent,
progressively dilating superficial veins. The veins of the lower limbs dilated first,
gradually becoming discolored and indurated (Panel A).
After 5 years, varicosities appeared on the anterior chest and abdominal wall (Panel
B). Gynecomastia, splenomegaly, and bilateral varicoceles also developed.
Jaundice, spider angiomata, and testicular atrophy were not seen.
There was no evidence of liver failure; however, a platelet count of 20,000 per cubic
millimeter indicated thrombocytopenia. Duplex Doppler ultrasonography of the
abdomen showed periportal fibrosis, splenomegaly, and high portal flow.
Esophagogastroduodenoscopy confirmed the presence of esophageal varices.
Viable eggs ofSchistosoma mansoni were found in stool specimens, which
confirmed the diagnosis of intestinal schistosomiasis leading to portal
hypertension and splenic sequestration.
He was treated with praziquantel and cleared the S. mansoni infection. Despite
evidence of profound portal hypertension, he has done well.
More than 200 million people worldwide are infected with schistosomes. Of these,
approximately 120 million have symptoms and 20 million are severely ill. During the
past decade, targeted interventions combining snail control, improved water quality,
and the treatment of infected persons have contributed to diminishing the burden of
disease.
Trematodes
chapter 55
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General characteristics
Trematodes are commonly called flukes
Are leaf shape worms which are generally flat and fleshy
Are hemophrodite except for schistosoma, which have separate
male and female
• Have complicated life cycle occuring in two or more host
• have operculated eggs( except for schistosoma) which
contaminated water, perpetuating the life cylce and which are
also used to diagnose infections.
• The first intermediate hosts are snails.
Trematodes
The most important trematodes are:
• Schistosoma species (blood flukes)
• Clonorchis (liver fluke)
• Paragonimus (lung fluke).
Schistosomes have by far the greatest
impact in terms of the number of people
infected, morbidity, and mortality.
SCHISTOSOMA
Disease: Schistosomiasis.
• Schistosoma mansoni, Schistosoma
japonicum affect the gastrointestinal
tract.
• Schistosoma haematobium affects the
urinary tract.
Epidemiology:
Approximately 250 million people are infected with
schistosomes and 600 million are at risk
SCHISTOSOMA Characteristics:
• Trematode (blood fluke). Adults exist as
two sexes but are attached to each other.
Eggs are distinguished by spines:
- Schistosoma mansoni has large lateral
spine.
- Schistosoma japonicum has small lateral
spine
- Schistosoma haematobium has terminal
spine
Male and female schistosomes
Schistosoma mansoni has large
lateral spine
Egg of Schistosoma japonicum
with small lateral spine
Schistosoma haematobium has
terminal spine.
Eggs of Schistosoma haematobium
with terminal spine
Free-swimming forked tail
cercariae
Life cycle of SCHISTOSOMA
• In the venous site, the female lays fertilizing eggs which
penetrate the gut or bladder wall.
• The eggs are excreted in the stool or urine and must
enter fresh water to hatch.
• Once hatched, the ciliated larvae (miracidia) penetrate
snails and undergo further development into sporocysts
and multiplication occurs to produce many freeswimming cercariae
• Humans are infected by free-swimming forked tail
cercariae that penetrate the skin.
• Cercariae form larvae ‘schistosomula’ that penetrate
blood vessels and are carried to the lung and the liver,
where they become adults flukes.
Schistosoma Pathogenesis:
Eggs in tissue induce inflammation,
granulomas, fibrosis, and obstruction,
especially
in
liver
and
spleen
hepatosplenomegaly.
• S. mansoni damages the colon (inferior
mesenteric venules)
• S. japonicum damages the small intestine
(superior mesenteric venules)
• S. haematobium damages the bladder
venules which can lead to carcinoma of
the bladder
Schistosoma Transmission:
• Transmitted by penetration of skin by
cercariae.
• Humans are definitive hosts; snails are
intermediate hosts.
• Endemic in tropical areas: S mansoni in
Africa
and
Latin
America,
S
haematobium in Africa and Middle East,
S japonicum in Asia
Schistosoma haematobium eggs in
section of bladder
Portal obstruction, in liver and
spleen (hepatosplenomegaly)
Schistosoma
Laboratory Diagnosis: Eggs visible in
feces or urine.
Treatment: Praziquantel.
Prevention: Proper disposal of human
waste.
Swimming in endemic areas
should be avoided.
Immunity:
• IL-4 and IL-5 induces B cells to classswitch to produces IgE.
• IL-5, which induces bone marrow
precursors to differentiate into
eosinophils
• IL-3 (along with IL-4), which stimulates
mast-cell growth.
• Ag / Ab activate complement.
Clonorchis sinensis
Disease: Clonorchiasis (chinese liver fluke)
Characteristics: Trematode (liver fluke).
Life cycle:
• Humans ingest undercooked fish containing encysted larvae
(metacercariae)
• In duodenum, immature flukes enter biliary duct, become adults,
and release eggs that are passed in feces.
• Eggs are eaten by snails; the eggs hatch and form larvae.
• These multiply through generations and then produce many freeswimming cercariae, which encyst under scales of fish and are
eaten by humans
Clonorchis sinensis adult
Clonorchis sinensis
Transmission:
• eating raw or undercooked freshwater fish.
• Humans are definitive hosts; snails and fish are first and second
intermediate hosts, respectively. Endemic in Asia.
Pathogenesis: Inflammation of biliary tract.
Laboratory Diagnosis: Brownish, small, operculated eggs visible
in feces.
Treatment:
Praziquantel.
Prevention:
waste.
Adequate cooking of fish. Proper disposal of human
Symptoms:
• irritation of the bile ducts which become
dilated and deviated.
• The liver may enlarge, become necrotic
and tender and its function may be impaired.
• Modest infections results in indigestion,
weakness and loss of weight.
• Heavier infections produce anemia, liver
enlargement, slight jaundice, edema, and
diarrhea.
Clonorchis sinensis operculated, brownish,
Small egg
Paragonimus Westermani
Disease: Paragonimiasis.
Characteristics: Trematode (lung
fluke).
LIFE CYCLE
• Humans ingest undercooked freshwater crab meat
containing encysted larvae (metacercariae).
• In gut, immature flukes enter peritoneal cavity, burrow
through diaphragm into lung parenchyma, and become
adults and produce eggs that enter bronchioles and are
coughed up or swallowed.
• Eggs in either sputum or feces that reach fresh water
hatch into miracidia that enter snails, multiply through
generations into larvae, and then form many freeswimming cercariae that infect and encyst in crabs.
Paragonimus Westermani
Transmission:
• Transmitted by eating raw or undercooked crab
meat.
• Humans are definitive hosts; snails and crabs
are first and second intermediate hosts,
respectively.
• Endemic in Asia and India.
Paragonimus westermani egg
Paragonimus Westermani
Pathogenesis: Inflammation and secondary
bacterial infection of lung.
Laboratory Diagnosis: Eggs visible in
sputum or feces.
Treatment: Praziquantel.
Prevention: Adequate cooking of crabs.
Proper disposal of human waste.
Features of medically important
trematodes
Serum creatinine concentration is used clinically as a convenient index
of kidney function, but it is important to remember that even a minimal
elevation in creatinine can reflect significantly decreased rate of
glomerular filtration.
Hematocrit (varies with altitude):
Male: 40.7-50.3%
Female: 36.1-44.3%
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Increased eosinophils (eosinophilia) is most often associated with allergic diseases and
parasites (such as worms). Possible disorders include:
eczema
leukemia
autoimmune diseases
asthma
hay fever
Medications that may cause an increase in eosinophils include:
amphetamines (appetite suppressants)
tranquilizers
bulk-type laxatives containing psyllium
certain antibiotics
Other minor
parasite
• Fasciola Hepatica(
sheep liver fluke)
• Acquisition
• Ingestion of aquatic
plants, water cress
• Reserviour: sheep,
cattle, humans
• Dz: subclical- fever,
nightsweats, malaise
• Rx: praziquantel
• Fasciolopsis buski (giant
intestinal fluke)
• Acquisition
• Ingestion of acquatic plants,
water chestnuts.
• Reserviour Host: pigs, dogs,
rabbits and humans
• Progression in humans
• Asymptomatic- abd pain and
diarrhea
• Dx: eggs in feces
• Rx: Praziquantel